ontraction joints (or control joints) are joints cut into a slab shortly after pouring. The purpose of these joints is to control the cracking of the slab as it cures. Most concrete slabs shrink and sometimes curl for the first 12 months after pouring. Contraction joints allow the slab to crack at predetermined intervals instead of natural random cracking. Joint filler is used to protect the joints from spalling and chipping caused by traffic on the slab.